Recently Identified Diagnostic Markers in Effusion Cytology

BACKGROUND: Effusion specimens are frequently encountered in cytopathology practice. As in surgical pathology, candidate markers for effusion diagnosis require thorough assessment prior to inclusion in diagnostic panels. This review discusses some of the currently used markers, with a focus on immunohistochemistry. SUMMARY: A literature search of relevant publications, with a focus on markers with an established diagnostic role. BRCA1-associated protein 1 (BAP1) and methylthioadenosine phosphorylase (MTAP) protein expression by immunohistochemistry has been shown to be useful in the differentiation of reactive mesothelial proliferations from mesothelioma, as well as in differentiating the latter from metastatic carcinoma, in multiple studies. Molecular analysis of CDKN2A, MTAP, BAP1, and NF2 status has been additionally applied to the differential diagnosis of mesothelioma from reactive mesothelium. Robust markers for the differentiation between mesothelioma and carcinoma, such as TAG-72/B72.3, claudin-4, calretinin and HEG1, are available, as are markers that support a specific origin for metastatic adenocarcinoma, such as PAX8, TTF1 and TRPS1. KEY MESSAGES: Effusion diagnosis remains central to staging, and consequently, prognosis of cancer patients. Effusions additionally constitute optimal material for predictive studies and thereby guide the choice of targeted therapy.